Abstract

The temporal relationship between cervical infection with Trichomonas vaginalis (TV) or human papillomavirus (HPV) and the incidence rate of cervical intraepithelial neoplasia grade three (CIN III) was examined in a cohort of 43,016 Norwegian women. From 1980 to 1989, a cervico-vaginal infection from TV and HPV was diagnosed cytologically in 988 and 678 women, respectively. During the 181,240 person-years of observation, 440 cases of CIN III/cervical cancer developed. The age-adjusted incidence rates (IR) of CIN III were 225 per 100,000 person-years among women with no cytologic evidence of infection, 459 among women with TV infection, and 729 among women with HPV infection. A multiple regression model yielded a relative rate (RR) of CIN III of 2.1 (95 percent confidence interval [CI] = 1.3-3.4) among women with TV infection and 3.5 (CI = 1.9-6.6) among women with HPV infection, compared with women with neither infection. As CIN can be misclassified as HPV infection, the entry Pap-smears of 10 women with HPV infection who later developed CIN III were re-examined. Excluding the four discordant cases with the corresponding person-years decreased the RR of CIN III to 2.1 (CI = 0.9-4.8). Our report demonstrates the limitations of studies that rely only on cytologic detection of HPV infection. Nevertheless, the results support the hypothesis that HPV is a causal factor for CIN III lesions, and also display an association between TV infection and cervical neoplasia.